Engineering a superwettable polyolefin membrane for highly efficient oil/water separation with excellent self-cleaning and photo-catalysis degradation property

Membrane technology has been intensively applied to the treatment of oily wastewater in recent years. Extensive progress has been made to design super-wetting membranes for separating stratified or emulsified oil/water mixtures. However, the membrane with small pore size is ineffective due to the severe decline of permeation, while the membrane with large pore size exhibits a poor separation efficiency for emulsion separation. Accordingly, a promising separation mechanism has been developed to improve the separation efficiency of the membrane with large pore size relying on the joint effect of demulsification and coalesce. Inspired by this strategy, a negatively charged superhydrophilic membrane is fabricated via the deposition of beta-FeOOH nanorods on the commercialized sulfonated polyolefin lithium-ion battery separators (LIBS). The abundant sulfo groups on the polyolefin surface offer enough binding sites to anchor beta-FeOOH nanorods. The fabricated membrane is qualified for separating stratified and emulsified oil/water mixtures, predominantly facilitated by the superwettability (underwater oil contact angle of 154 degrees and underwater oil rolling angle of 3 degrees) and the demulsification effect. A comprehensive oil/water separation performance of the composite membrane for the stratified and highly emulsified surfactant-free and surfactant-emulsified oil/water mixtures is obtained, with the respective permeation flux of up to 55503, 4112 and 1260 L m(-2) h(-1) and the corresponding separation efficiency of 99.9%, 99.2% and 98.7% solely driven by gravity. Moreover, considering the photo-Fenton catalysis of beta-FeOOH, the hybrid membrane exhibits an excellent self-cleaning property, good nanorods coating stability and superior dye degradation ability. More importantly, LIBS possess some unique advantages of commercial availability, chemical tolerance, good flexibility and excellent mechanical strength, which provides an attempt to explore a novel high-efficiency oil/water separation material.